Concerning a retractor for use with a seat belt to safely hold a passenger in the seat of a vehicle, an emergency lock type retractor is conventionally used, which includes an emergency lock mechanism to physically lock the retractor by the action of an inertia detecting means, which responds to a sudden acceleration, shock or deceleration of the vehicle, so that the passenger can be effectively and safely restrained in the seat.
For example, Unexamined Japanese Patent Publication No. 5-246303 discloses such an emergency lock type retractor, the lock means of which operates as follows. When a lock operating means which operates by the action of a deceleration detecting means (inertia detecting means) for detecting a deceleration in the case of an emergency of a vehicle makes the first and the second engaging member provided at both ends of a reel shaft (winding shaft) to engage with the first and the second portion to be engaged which are arranged in a frame (retractor base), it is possible to prevent the reel shaft from rotating in a direction in which the webbing is drawn out.
According to the lock means of the above retractor, a plurality of engaging members are synchronously engaged with the portions to be engaged which are formed on both side walls of the frame. Therefore, in the case of necessity, it is possible to positively lock the reel shaft so that the reel shaft can not rotate in a direction in which the webbing is drawn out from the retractor, and at the same time it is possible to provide a sufficiently high engaging force. Accordingly, the reliability of the emergency lock mechanism can be enhanced.
FIGS. 14a and 14b are views to explain the operation of a main pawl (first engaging member) 61 and a lock gear (lock operation means) 64 of the lock means disclosed in the above Unexamined Japanese Patent Publication. FIG. 14a is an enlarged view showing a primary portion of the main pawl 61 at a standby position, and FIG. 14b is an enlarged view showing a primary portion of the main pawl 61 at a lock position. FIG. 15 is a cross-sectional view showing an outline of the primary portion of the retractor.
A cam shape of the cam hole 64n of the lock gear 64 is shown by a phantom line in the drawing. In this case, the cam shape of the cam hole 64n is determined as follows. When the main pawl 61 is transferred from a state shown in FIG. 14a to a state of perfect lock shown in FIG. 14b by a relative rotation of the reel shaft 63 in the direction of .alpha., the main pawl 61 conducts a self-locking operation by the action of the teeth 62f of a side wall of the frame on a steep inclined plane side. The cam shape is determined so that the lock gear 64, which is denoted by the cam holes 64k, 64m and 64n in FIG. 14, can be a little reversed in the direction of .beta. by the cam follower 61f via the guide cam surface 64n.sub.2 of the cam hole 64n. When the cam shape of the cam hole 64n is determined as described above, in the case of a perfect engagement of the main pawl 61 with the teeth 62f, an engaging claw of the lever of the deceleration detecting means not shown can be released from the engagement with the teeth of the lock gear, so that the engaging claw of the lever of the deceleration detecting means can be put into a free condition.
That is, when the cam follower 61f is transferred from a standby position shown in FIG. 14a to a lock position shown in FIG. 14b, an acting force of the cam follower 61f is transmitted to the lock gear 64, so that the lock gear 64 is reversed in the direction of winding the webbing by the action of the guide cam surface 64n.sub.2. In this way, the lock gear reverse rotation control means is composed.
In this case, the lock operation means includes a reverse rotation control means by which the lock operation means is reversed by a predetermined amount of rotation in the direction of winding the webbing. By the reverse rotation of this lock operation means, the deceleration detecting means is put into a free condition. Accordingly, the occurrence of what is called an end lock state, which will be described below, can be prevented. When all the webbing, which has been drawn out, is suddenly wound by a spring force of the winding spring, the deceleration detecting means is operated by its shock, so that the rotation of the lock gear in the direction of winding the webbing can be checked. As a result, the webbing which is in a wound condition can be neither drawn out nor wound, which is defined as an end lock state. It is described that it is possible to prevent the occurrence of this end lock state.
In order to synchronously engage the main pawl 61 arrange at one end of the reel shaft 63 and the backup pawl 70 arranged at the other end, with the teeth 62f, 62g of the frame side walls, a joint pin 69, which is an engaging portion control means, penetrates the reel shaft 63. As shown in FIG. 15, a section of the main body 69a of the joint pin 69 is formed to be circular. An arm 69b extending in a direction perpendicular to the main body 69a is formed at the right end of the joint pin 69. A cam follower 69c whose section is circular is provided at an end of the arm 69b, so that the cam follower 69c can be guided by the cam hole 64m of the lock gear. A shaft portion 69d whose section is rectangular is formed at the left end of the main body 69a in the drawing. This rectangular shaft portion 69d is inserted into a hole formed at one end of the backup pawl 70 so that it can not be relatively rotated in the hole.
When the cam follower 69c is guided by the cam hole 64m so that the arm 69b is rotated, the main body 69a is rotated, and the rotation of the main body 69a is transmitted to the backup pawl 70. Therefore, the backup pawl 70 is rotated in accordance with the motion of the cam follower 69c guided by the cam hole 64m. Accordingly, the backup pawl 70 can be linked with the rotation of the main pawl 61 which is rotated in accordance with the motion of the cam follower 61f guided by the cam hole 64n of the lock gear.
Another lock means is disclosed, for example, in Unexamined Japanese Patent Publication No. 53-66621, which will be described below. In the belt retractor disclosed in the above patent publication, a winding shaft around which the webbing is wound is displaced to a lock position in the case of an emergency of a vehicle, and an engaging portion of at least one end portion of the winding shaft protruding from the retractor side wall is engaged with a portion to be engaged which is provided on the corresponding retractor side wall, so that the rotation of the winding wall can be checked.
FIG. 16 is a side view showing an outline of the structure of the above belt retractor. A U-shaped retractor base 160 includes a pair of side walls 161 which are opposed to each other. Openings 162 which are concentric to each other are formed on the pair of side walls 161. Gears 164 serving as engaging portions are provided at both end portions of the winding shaft 163 protruding from the openings 162 to the outside of the side wall. Short shafts 165 protruding from both sides of the winding shaft 163 are rotatably supported by the holes 168 on the shaft support plates 167 attached to the side walls 161, via the bushes 169. A hole 168 on the support plate 167 is larger than the outer diameter of the bush 169, so that the winding shaft 163 can be displaced to an upper lock position, however, the winding shaft 163 is pulled to the normal operating position, which is located at a left lower position in the drawing, by the action of a tension spring 166.
At the normal operating position, the gear 164 of the winding shaft 163 is not engaged with the engaging teeth 162a, which is a portion to be engaged, formed at the inner circumferential edge of the opening 162. Since the winding shaft 163 can be freely rotated, the webbing 171 wound around the winding shaft 163 can be freely drawn out.
In the case of an emergency of a vehicle such as a collision, the sensor device 170 is operated, and the winding shaft 163 is moved to an upper lock position, resisting a drawing force of the tension spring 166. Then the gear 164 is engaged with the engaging teeth 162a, so that the rotation of the winding shaft 163 can be prevented. Accordingly, the drawing of the webbing 171 can be prevented.
However, in the case of a retractor for use with a seat belt disclosed in the above Unexamined Japanese Patent Publication No. 5-246303, the lock gear reverse rotation control means for preventing the occurrence of an end lock state is composed of a guiding cam surface 64n.sub.2 of the cam hole 64n and a cam follower 61f. Therefore, a complicated reverse rotation controlling operation is conducted on the lock operation means. Accordingly, it is necessary to provide a complicated cam shape, and at the same time a high accuracy is required of the size of each component and further the assembling accuracy must be high.
The joint pin 69, which is a control means for controlling the engaging member, makes the teeth 62f and 62g formed on the side walls of the frame to simultaneously engage with the main pawl 61 and the backup pawl 70. This joint pin 69 must have the arm 69b, shaft 69d and cam follower 69c as described above. Therefore, the shape of the joint pin 69 becomes complicated. Further, due to the twisting rotation of the main body 69a, the joint pin 69 makes the main pawl 61 to link with the backup pawl 70. Therefore, when an excessively strong drawing force acts on the webbing and an impulsive torque is given to the joint pin 69, an impulsive twisting force is given to the base portion of the arm 69b and the shaft 69d with which one end of the backup pawl 70 is engaged. Accordingly, there is a possibility that these components are damaged.
Accordingly, concerning the lock operation means, it is necessary to enhance the mechanical strength of each component, and it is also necessary to severely manage the fluctuation of the size of each component and the assembling accuracy. Therefore, the manufacturing cost might be raised. In the lock means described in Unexamined Japanese Patent Publication No. 53-66621, when the engaging portion which is engaged with the portion to be engaged, provided on the retractor side wall, is arranged only at one end portion of the winding shaft, an engaging force to resist the drawing force of the webbing must be supported only by the side wall on one side even when an excessively strong tension is applied to the webbing in the case of a collision of a vehicle. For this reason, the mechanical strength required to the engaging portion and the portion to be engaged is increased, so that the degree of freedom of design is lowered.
In the case of the above belt retractor in which the engaging portion is engaged with the portion to be engaged when the winding shaft is displaced to the lock position in the case of an emergency of a vehicle, in order to hold the winding shaft 163, which is supported being capable of moving in the radial direction, at the normal position and stably conduct the winding and drawing operation, it is necessary to increase a spring force of the tension spring 166. Therefore, the size of the tension spring 166 is increased, and the frictional force of the short shaft 165 is increased. Consequently, the spacing efficiency of the retractor is deteriorated, and it is necessary to increase the winding capacity of the winding spring, and it is also necessary to enhance the machining accuracy and coating performance of the short shaft 165. In the case of a retractor in which the winding shaft is held at the normal operating position by a resin cover, the winding shaft is repeatedly displaced to prevent the webbing from being drawn out when the brake is suddenly applied in a case except for a collision of a vehicle. Accordingly, the resin cover is deteriorated and deformed, and there is a possibility that the accommodated sensors are damaged.
In the case of a winding shaft in which the body having the engaging portion is formed separately from the reel flange, in order to integrate the winding shaft with the reel flange, there is a possibility that the engaging portion of the winding shaft is not positively engaged with the portion to be engaged, on the retractor side wall unless the flange portion and the body are positioned with high accuracy.
Therefore, a first object of the present invention is to provide a highly efficient and inexpensive retractor for use with a seat belt, without using a complicated structure of the lock operation means which operates in the case of an emergency of a vehicle.
A second object of the present invention is to provide a highly efficient and inexpensive retractor for use with a seat belt, in which a pair of engaging elements arranged at both ends of the winding shaft can be simultaneously engaged with the portions to be engaged, on the retractor base.
A third object of the present invention is to provide a highly efficient retractor for use with a seat belt, having a lock means for obtaining a sufficiently high webbing engaging force even if the structure is simple.